Beginning SQL

Summary
Selecting Data from Different Tables
This chapter advanced your knowledge of joins far beyond the simple inner joins covered in Chapter 3.
You can now answer questions that were impossible to answer with a basic inner join. The chapter
started off by revisiting inner joins. It looked at how to achieve multiple joins with multiple conditions.
Additionally, this chapter covered the difference between equijoins, which use the equals operator, and
non-equijoins, which use comparison operators such as greater than or less than.
The chapter then turned to outer joins. Whereas inner joins require the ON condition to return true,
outer joins don’t. The chapter covered the following types of outer joins:
❑ Left outer joins, which return rows from the table on the left of the join, whether the ON clause is
true or not
❑ Right outer joins, which return rows from the table on the right, regardless of the ON clause
❑ Full outer joins, which return rows from the tables on both sides, even if the ON clause is false
In the final part of the chapter, you learned about how you can use the UNION statement to combine the
results from two or more SELECT queries into just one set of results.
The next chapter introduces the topic of subqueries and shows you how you can include another query
inside a query.
Exercises
1. List pairs of people who share the same favorite film category. The results set must include the
category name and the first and last names of the people who like that category.
2. List all the categories of film that no one has chosen as their favorite.
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